Characterization of Newly Accreted Soils On Reconstructed (LILA) Tree Islands in the Everglades.

Tree islands comprise a small area of the Everglades, but they are a vital element of the landscape. Hydrological modifications have affected tree islands, leading to a decrease in numbers, and extent. Tree islands' soils are higher in nutrient content, and rate of nutrient cycling compared to the marsh.

This research was conducted in the Loxahatchee Impoundment Landscape Assessment (LILA), located in Boynton Beach, FL. LILA recreates the main landscape features of the Everglades under semi-controlled hydrologic conditions. LILA tree islands were built using peat and limestone substrates. Soil accretion was evaluated using feldspar marker horizons. Soil accretion averaged 0.69 ± 0.84 cm yr^-1. Soils were evaluated by taking 10 cm cores on four islands. Cores were taken at two different elevations, on two different planting densities, and representing the two substrates. Cores were separated in two increments (0-3 cm), and (3-10 cm). The top increment (0-3) representing the newly accreted soil, based on estimates from marker horizons. The lower increment (3-10) represents soils that resemble the soil from which tree islands were constructed.   

Soils were analyzed for field bulk density (FBD), pH, organic matter (OM), total carbon, total nitrogen, and total phosphorus (TP). Additionally, fractions of water soluble P (WSP), exchangeable P (ex P), and Ca-Mg bound P were determined using sequential fractionation.

Results indicate that top soil has higher nutrient concentration, and OM compared to lower soil, i.e. TP differed from 374 ± 202 to 220 ± 132 µg g^-1 dw. Nutrients had a positive correlation to OM. Top soil on peat substrate islands had higher nutrient concentration, OM, and lower FBD compared to limestone islands. Concentrations of P fractions were higher on top soil compared to lower soil, and available P (WSP + ex P) was significantly higher (7.2% ± 2.5) at the top soil compared to the lower soil (6.2% ± 6.9).